This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for removing contaminants from a screen member operatively associated with a photoconductive member disposed therein.
As in all electrophotographic printing machines, the original document being reproduced is illuminated to form a light image thereof. The light image irradiates the charged portion of the photoconductive member dissipating selectively the charge thereon to record an electrostatic latent image. Heat settable particles develop the latent image. These particles are transferred to a sheet of support material, in image configuration. Thereafter, heat is applied to the particles permanently affixing them to the sheet of support material.
In the process of multi-color electrophotographic printing, a plurality of electrostatic latent images are recorded on the photoconductive member, each latent image corresponds to different color information in the original document. The latent images are developed with appropriately colored toner particles. The particles are then transferred to the sheet of support material in superimposed registration with one another. Thereafter, the resultant composite powder image is permanently affixed to the sheet of support material by the application of heat thereto forming a color copy of the original document.
Pictorial quality copies are reproduced in electrophotographic printing machine by employing half-tone imaging screens. The screen produces tone gradations by forming half-tone dots or lines of varying sizes. The dots increase in size from the highlight regions throughout the intermediate shades until merging together in the shadow regions. However, when this screen has contaminants deposited thereon, copy quality is degradated. These contaminants are more frequent in color electrophotographic printing machines than in black and white printing machines. This is due to the fact that a color printing machine will generally employ a plurality of differently colored developer materials, whereas black and white printing machines only utilize only black particles. It is evident that there is a significantly greater amount of particle contamination in color machines than in the black and white machines. Thus, the screen employed in a color printing machine is frequently contaminated and requires periodic cleaning.
Various types of brush cleaning devices have been developed for cleaning screens employed in electrophotographic printing machines. Typical screen cleaning systems are described in co-pending application Ser. No. 566,872 filed in 1975, and co-pending application Ser. No. 567,149 filed in 1975. Both of the foregoing applications relate to different types of brush cleaning mechanisms for use with a screen employed in an electrophotographic printing machine. However, even with brush cleaning systems of the type hereinbefore employed, the screen may still contain particle contaminants thereon.
Accordingly, it is the primary object of the present invention to improve the cleaning of a half-tone imaging screen employed in an electrophotographic printing machine.